11.2 Soil, Groundwater & Air Sampling Protocols and Chain of Custody
Key Takeaways
- For soil VOC analysis, follow the specified analytical method and project sampling plan; EPA Method 5035/5035A commonly uses discrete, hermetically collected portions with prescribed preservation to limit volatilization losses.
- Incremental Sampling Methodology (ISM) utilizes 30 to 100 multi-point aliquots per Decision Unit (DU) combined with specialized laboratory milling to provide unbiased, statistically defensible mean concentrations for non-volatile contaminants.
- Low-flow groundwater sampling uses minimal drawdown and project-defined stabilization criteria. A QAPP may adopt three readings at 3–5 minute intervals and benchmarks such as pH ±0.1, conductance ±3%, turbidity <10 NTU or ±10%, DO ±10% or ±0.2 mg/L, and ORP ±10 mV, but those numbers are not universal federal limits.
- Field QA/QC blanks verify data integrity: Trip Blanks evaluate VOC container shipping contamination, Equipment Rinsate Blanks assess field decontamination efficacy, and Field Blanks monitor ambient site atmospheric interference.
- Chain of Custody records sample possession and transfers and supports a defensible audit trail; it must be used with the project QAPP, preservation, custody seals, and laboratory receipt controls.
Soil, Groundwater & Air Sampling Protocols and Chain of Custody
Defensible environmental decision-making relies entirely upon the integrity, representativeness, and legal validity of field-collected samples. Improper sample collection, inadequate preservation, uncalibrated purging, cross-contamination, or a fractured chain of custody will invalidate laboratory analytical results and compromise regulatory compliance or courtroom proceedings.
A Certified Hazardous Materials Manager (CHMM) must master environmental media sampling methodologies across soil, groundwater, soil vapor, and ambient air, apply the governing project QAPP, approved sampling plan, analytical method, and regulatory program, and maintain documented Chain of Custody (COC) tracking.
1. Environmental Media Sampling Methodologies
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| ENVIRONMENTAL SAMPLING MEDIA MATRIX |
| |
| MEDIA | PRIMARY METHODOLOGY / STANDARD | CRITICAL FIELD CONTROLS |
| ----------------+----------------------------------------+--------------------------- |
| Soil (VOCs) | EPA Method 5035 / 5035A | Zero headspace, EnCore, |
| | (Hermetic Corers: EnCore, TerraCore) | Methanol/NaHSO4 or -7°C. |
| Soil (Metals / | Incremental Sampling Methodology (ISM) | 30-100 aliquots per DU, |
| SVOCs / PCBs) | (ITRC ISM-2 Standard) | Lab milling, subsampling. |
| Groundwater | EPA Low-Flow Purging & Sampling SOP | 100-500 mL/min, drawdown |
| | (Puls & Barcelona 1996) | <0.1 m, flow-through cell. |
| Soil Vapor / | EPA Method TO-15 / TO-15A | Passivated Summa Canister, |
| Ambient Air | (Evacuated Stainless Steel Canisters) | He leak shroud, flow reg. |
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Soil Sampling Methodologies
1. Discrete (Grab) vs. Composite Sampling
- Discrete (Grab) Sampling: A single sample collected from a specific spatial location and depth interval. used for VOC analysis when required by the governing method or sampling plan because mixing, homogenization, or headspace exposure can cause loss of volatile analytes.
- Composite sampling: Combines multiple soil aliquots to estimate an average for suitable nonvolatile analytes. Do not composite VOC samples when the governing method or QAPP requires discrete hermetic portions, because mixing and headspace can cause volatilization loss.
2. EPA Method 5035 / 5035A (Volatile Organic Soil Collection)
When EPA Method 5035/5035A is the selected method for VOC soil samples, follow its specified collection, preservation, container, and holding procedures, including:
- Zero-Headspace Core Samplers: Using dedicated airtight coring devices (e.g., EnCore, TerraCore, EasyDraw Syringe) to collect intact 5-gram soil plugs extruded directly into pre-weighed, hermetically sealed VOA vials with Teflon-lined septa.
- Preservation Regimes:
- Low-Level VOCs ($< 200,\mu\text{g/kg}$): Preserved in vials containing acidified water (Sodium Bisulfate, $\text{NaHSO}_4$) or unpreserved water frozen immediately to $-7^\circ\text{C}\text{ to }-20^\circ\text{C}$ within 48 hours.
- High-Level VOCs ($> 200,\mu\text{g/kg}$): Preserved in vials containing purge-and-trap grade Methanol ($\text{CH}_3\text{OH}$), which extracts VOCs into the solvent phase.
- All samples must be chilled to $4^\circ\text{C} \pm 2^\circ\text{C}$ immediately upon collection.
3. Incremental Sampling Methodology (ISM)
Developed by the Interstate Technology & Regulatory Council (ITRC), ISM is a structured sampling protocol designed to eliminate spatial heterogeneity errors in particulate media (soils and sediments):
- A target area is designated as a Decision Unit (DU) (e.g., exposure unit, source area).
- 30 to 100 discrete increments (aliquots) of equal mass are collected across a systematic random grid throughout the DU and combined into a single 1-kilogram composite.
- The laboratory dries, sieves, and mechanically mills (pulverizes) the entire sample to $< 2,\text{mm}$ (or $< 250,\mu\text{m}$) before extracting a representative 2D subsample.
- Provides an unbiased, statistically defensible estimate of the true mean concentration across the DU with vastly superior reproducibility compared to traditional grab sampling.
2. Groundwater Monitoring Well Construction & Purging Protocols
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| GROUNDWATER MONITORING WELL SCHEMATIC |
| |
| [Surface Completion] ---> Flush-Mount Vault / Stick-Up Steel Protective |
| Casing with Locking Sanitary Cap & Sloped Apron |
| |
| [Upper Annulus] ---> Cement-Bentonite Grout Seal |
| (Tremie pipe placed from bentonite seal up) |
| |
| [Bentonite Seal] ---> Hydrated Bentonite Pellet/Chip Seal |
| (2 to 3 ft thick, prevents grout infiltration) |
| |
| [Filter Pack] ---> Clean 20/40 Silica Sand Filter Pack |
| (Extends 1 to 2 ft above top of well screen) |
| |
| [Well Screen] ---> Factory-Slotted PVC or 316 Stainless Screen |
| (0.010-inch / 10-slot across water table) |
| |
| [Well Sump] ---> Threaded Bottom Cap / Sediment Sump |
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Low-Flow (Minimal Drawdown) Purging & Sampling (EPA SOP)
Introduced by Puls and Barcelona (1996), Low-Flow purging isolates the screened interval and draws formation water directly from the aquifer through the well screen, eliminating the need to purge the entire stagnant casing volume.
Operational Parameters:
- Pumping Rate: Maintained between $100\text{ to }500,\text{mL/min}$ using an adjustable-rate bladder pump or low-flow submersible pump positioned at the midpoint of the saturated screen.
- Drawdown Limit: Water level drawdown must be continuously monitored with an electronic water level meter and maintained at $< 0.1,\text{meter}$ ($< 0.33,\text{ft}$).
- In-Line Flow-Through Cell: Groundwater is routed through a sealed multi-parameter flow-through cell to monitor water quality indicator parameters without atmospheric contact.
Low-Flow Stabilization Criteria:
The project QAPP or sampling plan must specify the stabilization rule. A commonly used low-flow procedure allows sampling after three consecutive readings, recorded at 3- to 5-minute intervals, meet the following project-selected benchmarks; these values are guidance conventions, not universal federal limits:
| Indicator Parameter | Stabilization Benchmark | Technical Significance |
|---|---|---|
| pH | $\mathbf{\pm 0.1}$ standard units | Chemical equilibrium and acid-base conditions. |
| Specific Conductance | $\mathbf{\pm 3%}$ of reading | Dissolved ionic solids concentration equilibrium. |
| Turbidity | $\mathbf{< 10,\text{NTU}}$ or $\mathbf{\pm 10%}$ (if $> 10,\text{NTU}$) | Ensures suspended colloids are not artificially elevating metals concentrations. |
| Dissolved Oxygen (DO) | $\mathbf{\pm 10%}$ or $\mathbf{\pm 0.2,\text{mg/L}}$ (whichever greater) | Redox conditions (critical for biological/chemical stability). |
| Oxidation-Reduction (ORP) | $\mathbf{\pm 10,\text{mV}}$ | Electrochemical electron activity and redox regime. |
| Temperature | $\mathbf{\pm 3%}$ of reading | Informational (confirms formation vs. surface heating). |
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| COMPARISON OF GROUNDWATER PURGING METHODOLOGIES |
| |
| METHOD | ADVANTAGES | DISADVANTAGES |
| ------------------------+----------------------------+------------------- |
| Low-Flow (Micro-Purge) | - Highly representative | - Requires delicate|
| (EPA SOP) | - Low turbidity (<10 NTU) | flow adjustments |
| | - Minimal waste purge vol | - Longer setup time|
| ------------------------+----------------------------+------------------- |
| Traditional Purge | - Simple field execution | - High turbidity |
| (3 to 5 Well Volumes) | - Standard bailer use | - VOC stripping |
| | | - Large purge waste|
| ------------------------+----------------------------+------------------- |
| Passive Diffusion Bag | - Zero purge water waste | - VOCs ONLY |
| (PDB Sampler) | - Rapid deployment | - Ineffective for |
| | - Low equipment cost | metals/inorganics|
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3. Soil Vapor & Ambient Air Sampling (EPA Method TO-15)
Vapor intrusion investigations evaluate the migration of volatile chemical vapors from contaminated subsurface soil and groundwater into overlying building structures.
Summa Canister Sampling
- Summa Canisters: Passivated (electropolished and silica-lined) stainless steel vessels cleaned, certified leak-free, and evacuated by the laboratory to high vacuum (approximately $-29\text{ to }-30,\text{in. Hg}$ or $< 10,\text{Pa}$). Available in $6,\text{L}$ (ambient/indoor air) and $1,\text{L}$ (soil gas) sizes.
- Critical Orifice Flow Controllers: Calibrated flow restrictors attached to the canister inlet to ensure constant air intake over a fixed duration:
- 8-Hour Flow Controller: OSHA workplace / industrial occupational exposure assessments.
- 24-Hour Flow Controller: Residential indoor and outdoor ambient air risk assessments.
- 10- to 30-Minute Flow Controller: Subsurface soil gas screening.
- Analytical Protocol: EPA Method TO-15 / TO-15A (Determination of Volatile Organic Compounds in Ambient Air by Gas Chromatography / Mass Spectrometry).
Sub-Slab Vapor Pin Installation & Leak Testing
To prevent ambient indoor air from short-circuiting into the subsurface soil vapor sample:
- A brass or stainless steel Vapor Pin with an expandable silicone sleeve is hammer-drilled and sealed through the concrete slab.
- Helium Shroud Leak Test: A containment shroud is placed over the wellhead and enriched with helium gas ($> 20%\text{ He}$). A portable helium detector draws air from the vapor probe. The project protocol establishes an acceptance criterion, often helium in the sample stream below $5%\text{ to }10%$ of the shroud concentration; exceeding that criterion indicates a leak that must be corrected before sampling.
4. Field Quality Assurance / Quality Control (QA/QC) Samples
Field QA/QC samples isolate and quantify error introduced during sampling, decontamination, sample transport, and laboratory processing.
| QA/QC Sample Type | Preparation & Media | Evaluation Target / Objective | Typical / QAPP-Specified Frequency |
|---|---|---|---|
| Trip Blank | Laboratory-grade deionized water in $40,\text{mL}$ VOA vials; remains sealed in shipping cooler at all times. | Evaluates VOC cross-contamination during transit, container handling, and cooler storage. | 1 per shipping cooler containing VOC samples. |
| Equipment / Rinsate Blank | Analyte-free DI water poured over/through decontaminated non-dedicated field equipment. | Evaluates effectiveness of field equipment decontamination and cross-contamination between boreholes. | 1 per day or 1 per 20 samples per equipment type. |
| Field Duplicate | Co-located sample collected simultaneously or consecutively from same sampling point; labeled blindly. | Evaluates field sampling precision, matrix homogeneity, and laboratory analytical repeatability. | 1 per 10 or 1 per 20 samples ($5%\text{ to }10%$). |
| Field Blank | Analyte-free DI water transferred between containers at the open-air sampling location. | Evaluates ambient atmospheric air contamination at the active sampling site. | 1 per sampling event or as defined in QAPP. |
| Matrix Spike / Matrix Spike Duplicate (MS/MSD) | Field sample split in lab and spiked with known target analyte mass (requires triple sample volume in field). | Evaluates analytical accuracy (% Recovery), precision (RPD), and matrix interference/effects. | 1 per 20 field samples ($5%$ frequency). |
| Temperature Blank | Small plastic or glass vial of tap water placed in cooler. | Read with IR thermometer upon lab receipt to verify preservation temperature ($4^\circ\text{C} \pm 2^\circ\text{C}$). | 1 per shipping cooler. |
5. Chain of Custody (COC) Record & Legal Integrity
The Chain of Custody (COC) record documents sample possession and transfers from collection through laboratory receipt and disposition. A complete record supports traceability and legal defensibility, but it does not by itself establish admissibility or prove that every handling step was proper.
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| COMMON CHAIN OF CUSTODY (COC) CONTROLS |
| |
| A sample is legally in "CUSTODY" if it is: |
| 1. In the sampler's actual physical possession; OR |
| 2. In the sampler's continuous unobstructed view; OR |
| 3. Placed in a secure, locked area accessible ONLY to authorized staff; OR|
| 4. Sealed in a shipping container with signed, intact tamper-evident tape.|
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Core Fields on a Project-Approved Chain of Custody Form:
- Unique Sample ID: Distinct alphanumeric identifier matching container labels exactly.
- Sampling Date & Military Time: Precise collection timestamp (e.g.,
2026-08-15 14:35). - Sample Matrix: Specific media designation (Soil, Groundwater, Wastewater, Soil Gas, Sludge).
- Sample Type: Indication of Discrete (Grab) or Composite.
- Container Count & Type: Total number and composition (e.g., $3 \times 40,\text{mL}$ VOA vials, $1 \times 1,\text{L}$ Amber glass, $1 \times 500,\text{mL}$ Poly).
- Preservatives Added: Specified chemical preservatives ($\text{HNO}_3$, $\text{HCl}$, $\text{H}_2\text{SO}_4$, $\text{NaOH}$, Methanol, or None / Chilled $4^\circ\text{C}$).
- Requested Analytical Methods: Exact EPA SW-846 method numbers (e.g., EPA 8260D VOCs, EPA 6020B Metals, EPA 8270E SVOCs).
- Custody Transfer Signatures: Sequential "Relinquished By" and "Received By" signatures, dates, and times for every individual who handled the shipment.
A project QAPP adopts the following low-flow acceptance rule: three consecutive readings 3–5 minutes apart must meet pH ±0.1, conductance ±3%, turbidity <10 NTU or ±10%, DO ±0.2 mg/L or ±10%, and ORP ±10 mV, while drawdown remains below 0.1 m. During purging of MW-4 at 250 mL/min, the technician records:
An environmental field team is collecting soil samples to delineate the horizontal and vertical extent of a benzene and xylenes release at an active bulk fuel terminal. Which soil collection procedure is required by EPA Method 5035A to ensure defensible analytical data?
A laboratory analytical report for a groundwater investigation shows that methylene chloride was detected at $12,\mu\text{g/L}$ in monitoring well MW-2 and at $14,\mu\text{g/L}$ in the accompanying Trip Blank. Methylene chloride was not detected in the Equipment Rinsate Blank. How must the CHMM interpret these results?
Prior to opening an evacuated Summa canister to collect an 8-hour sub-slab soil vapor sample inside an active manufacturing plant, what quality assurance step must be executed to ensure indoor air does not short-circuit into the sub-slab probe?